Confused

1971 cj5 with 225 V6. mostly original. 4:88 in the rear and 4:89 in the model 27 up front. I was having some binding up noise coming from the front end in Moab. So I put the jeep on jack stands, put it in 4wd low and in gear and ran the motor. What seemed weird to me is the front tire was spinning faster than the rear tires. On the dirt road when I drove it in 4wd I did not notice anything. Does is sound normal to you guy's. I tried to download a 11 second video however it would not download. You can view the video om my facebook page. julius vatalaro

https://www.facebook.com/video.php?v=1861203497331934

 

How do you know the ratios? You can look at the edge of the ring gear to see the tooth counts, ie "41 11" will be 41/11 = 3.73. Note that if you compare a posi rear end to an open front, both rear wheels with posi between them will spin at one speed and the single moving front tire with an open axle will spin at twice that speed.

 

The tag on the diff's are correct. Rear 4:88 Front 4:89. The rear has a power-lok and both tires spin in the same direction, the front is open and the tire on the drivers side spins. So what Timgr say's may be why. Did you both see the video? To whatch the video look at my post and it says watch on facebook.

 

I didn't see the video, but by the nature of spider and side gears, I can totally see how one end would run faster than the other if only one tire was running in the front. I think spider/sides have a 2:1 ratio? So either it makes it run twice as fast or half as fast depending.

 

I think this is what's happening. The .01 ratio difference is a non issue, I've seen factory built trucks with up to .04 different ratios.

 

My 1st vehicle ever, 71 Ford F100 w/360, NP435,D21 tcase (single speed) , 4.14 rear, 4.11 front.

 

I tried to get it to bind up again with no success.

 

Sometimes even with an open diff the front end will find a little bit when turning this could be what was happening.

 

will 0.01 make a difference between the front and rear diff's?

just a slight change in tire pressure will cause a greater difference than that.

 

If your tires are planted on a firm surface the drivetrain will tighten up due to different number of revs when turning. You'll have a heck of a time shifting out of 4WD or unlocking hubs until you get on some sand, gravel, dirt, grass, mud. Pictures Ive seen of Moab shows a lot of smooth clean rock.

I wouldnt sweat it ao long as you occasionally get on a surface that allows some slip. Mom drove us kids to the store one day around 1975. Dad had left the hubs locked and in 4H, she had that sucker wrapped tight. I remember her furiously kicking and jerking that lever. And we wonder why the mechanisms are sloppy. Sorry, it was Mom.

 

No.

Tire pressure does not change axle ratios. That's a myth.

 

+1

Even an open front differential will bind up if there's no slippage. The motion is never lost - it has to go somewhere. The left wheel can turn slower than the right and vice-versa, but the sum of both wheel's turns is fixed by the engine speed and axle ratio. Going around a corner changes the length of the paths for the inner and outer wheel which when added are not the same as when straight ahead. There has to be some slippage or there will be binding. This is why the owner's manual says never to use 4WD on pavement.

 

I guess when I said binding I was wrong it is more like a clunking sound. I am thinking the front axle on the left or the hub. It's like metal to metal. Not the binding you get from being in 4wd on pavement. I think it is something internal, however I will need to tear into it and see if I find metal shavings. I will let you know what I find. I am sure it is the front end drivers side.

 

Last description would lead me to an axle u-joint. Sometimes the joint will get dry and tight one direction and sloppy loose the other way. The axle will lunge as the joint flops from loose to tight while in a turn, but will seem more or less OK when straight. It will be very noticeable in the steering wheel. Does that describe your symptoms?

 

I never stated that a change in tire pressure will change axle ratio's. a change in tire pressure will change the circumfrence of tire. a very limited amount but it does change it. in many forms of motor sport the mechanics check tire pressure and tire circumfrence. they also shave tires as well. so that tires maintain a desired circumfrence. even more critical in a diff with a locker of some sort.

It does not change the axle ratio. does a change in pressure( a change in tire diameter/circumfrence) change axle ratio? no; but it can make a bigger difference than the .01 difference in a ratio. which could also be a simple matter of round of numbers in the mathematics of the formula rather than a physical dimention of ring and pinion or the tire circumfrence

 

Well, the demonstrations I have seen yield no measurable difference in circumference. Maybe for a huge change in pressure... I will measure myself some day. Tire wear yes. For example, a WJ Grand Cherokee with Quadradrive should have identical tires all around, and worn to the same degree (rotation required!)

It's a common practice to mix, say 4.09s with 4.11s or 4.10s. I'm sure you realize this comes from the limited number of tooth count combinations possible with a given ring gear diameter. Integers only need apply.

 

I think my nest move will be to look inside for some worn pieces. When I did my restoration I did not replace the front axle u-joints. I know the hubs are brand new.